Liquid-crystal medium, and electro-optical display containing same

ABSTRACT

The present invention relates to nematic liquid-crystal media which comprise  
     a) a dielectrically negative, liquid-crystalline component A comprising one or more compounds of the formula I  
                 
 
      in which the parameters are as defined in the text, and  
     b) a dielectrically negative, liquid-crystalline component B, and optionally  
     c) a dielectrically neutral, liquid-crystalline component C, and optionally  
     d) a dielectrically positive, liquid-crystalline component D,  
     and to the use of these media in liquid-crystal displays, and to liquid-crystal displays which use these media, in particular VAN and IPS displays.

[0001] The present invention relates to liquid-crystal displays,particularly active matrix addressed liquid-crystal displays (AMDs orAMLCDs), especially those which use an active matrix comprising thinfilm transistors (TFTs) or varistors. In addition, the presentapplication relates to liquid-crystal media for use in displays of thistype. AMDs of this type are able to use various active electronicswitching elements. The most widespread are displays which usethree-pole switching elements. These are also preferred in the presentinvention. Examples of three-pole switching elements of this type areMOS (metal oxide silicon) transistors or the above-mentioned TFTs orvaristors. In the TFTs, various semiconductor materials, predominantlysilicon or alternatively cadmium selenide, are used. In particular,poly-crystalline silicon or amorphous silicon is used. In contrast tothe three-pole electronic switching elements, matrixes of 2-poleswitching elements, such as, for example, MIM (metal insulator metal)diodes, ring diodes or “back to back” diodes, can also be employed inAMDs. However, as also explained in greater detail below, these aregenerally not preferred owing to the worse electro-optical propertiesachieved by the AMDs.

[0002] The liquid crystals used as dielectrics in liquid-crystaldisplays of this type are those whose optical properties changereversibly on application of an electric voltage. Electro-opticaldisplays which use liquid-crystals as media are known to the personskilled in the art. These liquid-crystal displays use variouselectro-optical effects.

[0003] The most widespread conventional displays use the TN effect(twisted nematic, having a nematic structure which is twisted by about90°), the STN effect (supertwisted nematic) or the SBE effect(supertwisted birefringence effect). In these and similarelectro-optical effects, liquid-crystalline media of positive dielectricanisotropy (Δε) are used.

[0004] Since the operating voltage in displays in general, i.e.including in displays using these effects, should be as low as possible,use is made of liquid-crystal media of large dielectric anisotropy,which are generally composed predominantly of dielectrically positiveliquid-crystal compounds and at most comprise relatively small/lowproportions of dielectrically neutral compounds.

[0005] In contrast to the conventional displays utilizingelectro-optical effects which require liquid-crystal media of positivedielectric anisotropy, there are other electro-optical effects which useliquid-crystal media of negative dielectric anisotropy, such as, forexample, the ECB effect (electrically controlled birefringence) and itssub-forms DAP (deformation of aligned phases), VAN (vertically alignednematics) and CSH (colour super homeotropics). These are thesubject-matter of the present application.

[0006] The IPS (in plane switching) effect, which has been employed toan increased extent recently, can use both dielectrically positive anddielectrically negative liquid-crystal media, similarly to “guest/host”displays, which can employ dyes either in dielectrically positive or indielectrical negative media, depending on the display mode used. In thecase of the liquid-crystal displays mentioned in this paragraph, thosewhich use dielectrically negative liquid-crystal media are also thesubject-matter of the present application.

[0007] A further highly promising type of liquid-crystal display areso-called “axially symmetric microdomain” (abbreviated to ASM) displays,which are preferably addressed by means of plasma arrays (plasmaaddressed liquid crystal displays, or PA LCDs). These displays are alsothe subject-matter of the present application.

[0008] The liquid-crystal media employed in the above-mentionedliquid-crystal displays and all liquid-crystal displays which utilizesimilar effects generally consist predominantly and in most cases evenvery substantially of liquid-crystal compounds having the correspondingdielectric anisotropy, i.e. of compounds of positive dielectricanisotropy in the case of dielectrically positive media and of compoundsof negative dielectric anisotropy in the case of dielectrically negativemedia.

[0009] In the media used in accordance with the present application, atmost significant amounts of dielectrically neutral liquid-crystalcompounds and in general only very small amounts or even nodielectrically positive compounds at all, are typically employed, sincein general the liquid-crystal displays should have the lowest possibleaddressing voltages. For this reason, liquid-crystal compounds havingthe opposite sign of the dielectric anisotropy to the dielectricanisotropy of the medium are generally employed extremely sparingly ornot at all.

[0010] The liquid-crystal media of the prior art have relatively lowlow-temperature stabilities. Thus, the nematic phases often extend onlydown to −20° C. and in some cases even only down to −10° C. In addition,the threshold voltages (V₀) are at the same time relatively high, inmost cases even greater than 2 V.

[0011] For the most part, the liquid-crystal media of the prior art haverelatively unfavourable values for Δn, which are often greater than0.10. However, such large Δn values are not particularly advantageousfor VAN displays, since small values for the optical retardation aretypically used in VAN displays. Thus, for example, a d·Δn ofapproximately 0.30 μm is employed in the case of an untwisted directororientation or a d·Δn of approximately 0.40 μm is employed with a 90°twist. Such large Δn values require the realization of very small layerthicknesses, which, although favorable for the response times observed,result, however, in low production yields.

[0012] In most cases, the most favorable Δn values for practicaldisplays are in the range from 0.07 to 0.12. This also applies to IPSdisplays.

[0013] In addition, the response time of the prior-art displays is ofteninadequately long, in particular for video-capable displays. Thus, theviscosities of the liquid-crystal media must be improved, i.e. reduced.This applies in particular to the rotational viscosity and veryparticularly at low temperatures. A reduction in the flow viscositygenerally results, in particular in the case of displays having ahomeotropic edge alignment of the liquid crystals (for example in ECBand VAN displays), in a shortening of the filling times duringproduction of the displays.

[0014] Thus, there has been and continues to be a great demand forliquid-crystal media which do not have the disadvantages of the mediafrom the prior art or at least do so to a significantly reduced extent.

[0015] Surprisingly, it has been found that this is achieved by theliquid-crystal media according to the invention. These media comprise

[0016] a) a dielectrically negative, liquid-crystalline component(component A) which comprises one or more dielectrically negativecompound(s) of the formula I

[0017]  in which

[0018]  and, independently of one another, are

[0019]  preferably, independently of one another, are

[0020]  particularly preferably

[0021] R¹¹ is alkyl having from 1 to 7 carbon atoms, preferably n-alkyl,particularly preferably n-alkyl having from 1 to 5 carbon atoms, alkoxyhaving from 1 to 7 carbon atoms, preferably n-alkoxy, particularlypreferably n-alkoxy having from 1 to 5 carbon atoms, or alkoxy-alkyl,alkenyl or alkenyloxy having from 2 to 7 carbon atoms, preferably havingfrom 2 to 4 carbon atoms, preferably alkenyloxy,

[0022] R¹² is alkyl or alkoxy having from 1 to 7 carbon atoms,preferably alkoxy, preferably n-alkoxy and particularly preferablyn-alkoxy having from 2 to 5 carbon atoms, or alkoxyalkyl, alkenyl oralkenyloxy having from 2 to 7 carbon atoms, preferably having from 2 to4 carbon atoms, preferably alkenyloxy, one of

[0023] Z¹¹ and Z¹² is OCF₂ or CF₂O and the other is a single bond, and

[0024] n is 0 or 1, and

[0025] b) a dielectrically negative, liquid-crystalline component(component B), which preferably comprises one or more dielectricallynegative compounds(s) selected from the group consisting of thecompounds of the formulae II and III

[0026]  in which

[0027] R²¹ is alkyl having from 1 to 7 carbon atoms, preferably n-alkyland particularly preferably n-alkyl having from 1 to 5 carbon atoms,alkoxy having from 1 to 7 carbon atoms, preferably n-alkoxy andparticularly preferably n-alkoxy having from 2 to 5 carbon atoms, oralkoxyalkyl, alkenyl or alkenyloxy having from 2 to 7 carbon atoms,preferably having from 2 to 4 carbon atoms, preferably alkenyloxy,

[0028] R²² is alkyl having from 1 to 7 carbon atoms, preferably n-alkyl,particularly preferably n-alkyl having from 1 to 3 carbon atoms, alkoxyhaving from 1 to 7 carbon atoms, preferably n-alkoxy, particularlypreferably n-alkoxy having from 2 to 5 carbon atoms, or alkenyloxyhaving from 2 to 7 carbon atoms, preferably having from 2 to 4 carbonatoms,

[0029] Z²¹ and Z²² are each, independently of one another, —CH₂—CH₂—,—CH═CH—, —C≡C—, —COO— or a single bond, preferably —CH₂—CH₂— or a singlebond and particularly preferably a single bond,

[0030]  are each, independently of one another,

[0031]  preferably

[0032]  and, if present,

[0033] L²¹ and L²² are both C—F or one of the two is N and the other isC—F, preferably both are C—F, and

[0034] m is 0 or 1,

[0035]  are each, independently of one and another, as defined above for

[0036]  respectively in the case of the formula II,

[0037] z³ is —CH₂—CH₂—, —CH═CH—, —C≡C—, —COO=13 or a single bond,preferably —CH₂—CH₂— or a single bond and particularly preferably asingle bond,

[0038] R³¹ and R³² are each, independently of one another, alkyl havingfrom 1 to 7 carbon atoms, preferably n-alkyl and particularly preferablyn-alkyl having from 1 to 5 carbon atoms, alkoxy having from 1 to 7carbon atoms, preferably n-alkoxy and particularly preferably n-alkoxyhaving from 2 to 5 carbon atoms, or alkenyloxy having 2 to 7 carbonatoms, preferably having from 2 to 4 carbon atoms, and

[0039] I is 1 or 2,

[0040]  and optionally

[0041] c) a dielectrically neutral component (component C) whichcomprises one or more dielectrically neutral compound(s) of the formulaIV

[0042]  in which

[0043] R⁴¹ and R⁴² are each, independently of one another, as definedabove for R²¹ in the case of the formula II,

[0044] Z⁴¹, Z⁴² and Z⁴³ are each, independently of one another,—CH₂CH₂—, —CH═CH—, —COO— or a single bond,

[0045]  are each, independently of one another,

[0046]  o and p, independently of one another, are 0 or 1, the variablesin formula IV are preferably

[0047] R⁴¹ and R⁴² are each, independently of one another, alkyl oralkoxy having 1-5 carbon atoms or alkenyl having 2-5 carbon atoms,

[0048]  are each, independently of one another,

[0049]  and very particularly preferably at least two of these rings

[0050]  where two adjacent rings are very particularly preferably linkeddirectly to one another, preferably

[0051]  or

[0052]  and optionally

[0053] d) one or more dielectric positive compound(s) of the formula V

[0054]  in which

[0055] R⁵ is alkyl or alkoxy having from 1 to 7 carbon atoms, oralkoxyalkyl, alkenyl or alkenyloxy having from 2 to 7 carbon atoms,

[0056] Z⁵¹, Z⁵² and Z⁵³ are each, independently of one another,—CH₂—CH₂—, —CH═CH—, —C≡C—, —COO— or a single bond,

[0057]  are each, independently of one another,

[0058] X⁵ is F, OCF₂H or OCF₃, and

[0059] Y⁵ is H or F, preferably F in the case where X=F or OCF₂H, and

[0060] q and r are each, independently of one another, 0 or 1.

[0061] In a further preferred embodiment, the medium comprises one ormore dielectrically negative compounds of the formula VI

[0062] in which

[0063] R⁶¹ and R⁶² are alkyl having from 1 to 7 carbon atoms, preferablyn-alkyl and particularly preferably n-alkyl having from 1 to 5 carbonatoms, alkoxy having from 1 to 7 carbon atoms, preferably n-alkoxy andparticularly preferably n-alkoxy having from 2 to 5 carbon atoms, oralkenyloxy having from 2 to 7 carbon atoms, preferably having from 2 to4 carbon atoms, very particularly preferably both are n-alkoxy havingfrom 1 to 5 carbon atoms,

[0064] Z⁶ is as defined above for Z²¹ in the case of the formula II,

[0065] L⁶¹ and L⁶² are both C—F or one of the two is N and the other isC—F, and

[0066] L⁶³ and L⁶⁴ are both C—F or one of the two is N and the other isC—F.

[0067] In a further preferred embodiment, the medium comprises one ormore dielectrically negative compounds of the formula VII

[0068] in which

[0069] R⁷¹ and R⁷² are alkyl having from 1 to 7 carbon atoms, preferablyn-alkyl and particularly preferably n-alkyl having from 1 to 5 carbonatoms, alkoxy having from 1 to 7 carbon atoms, preferably n-alkoxy andparticularly preferably n-alkoxy having from 2 to 5 carbon atoms, oralkenyloxy having from 2 to 7 carbon atoms, preferably having from 2 to4 carbon atoms, very particularly preferably both are n-alkoxy havingfrom 1 to 5 carbon atoms, and

[0070] L⁷¹ and L⁷² are both C—F or one of the two is N and the other isC—F.

[0071] Component A preferably consists predominantly, particularlypreferably consists essentially completely and very particularlypreferably consists virtually completely, of one or more compounds ofthe formula I. These compounds of the formula I are preferably selectedfrom the group consisting of the compounds of the formulae I-1 to I-8:

[0072] in which

[0073] R¹¹, R¹² and Z¹² are each as defined above under the formula I.

[0074] The compounds of the formula I are particularly preferablyselected from the group consisting of the compounds of the followingsixteen formulae I-1a to I-8b:

[0075] in which

[0076] R¹¹ and R¹² are as defined above under the formula I, and R¹¹ ispreferably alkyl having from 1 to 7 carbon atoms or alkenyl having from2 to 7 carbon atoms, and R¹² is preferably alkoxy having from 1 to 7carbon atoms or alkenyloxy having from 2 to 7 carbon atoms.

[0077] The compounds are very particularly preferably selected from thegroup consisting of the compounds of the formulae I-1a, I-1b, I-2a,I-3a, I-4a, I-4b, I-5a, I-6a, I-6b and I-7a and in particular from thegroup consisting of the compounds of the formulae I-1b and I-7a.

[0078] In the present application, in connection with the quoting of theconstituents of the compositions:

[0079] comprise means that the concentration of the relevantconstituents in the composition is preferably 10% or more, particularlypreferably 20% or more,

[0080] consist predominantly of means that the concentration of therelevant constituents in the composition is preferably 50% or more,particularly preferably 55% or more and very particularly preferably 60%or more,

[0081] consist essentially completely of means that the concentration ofthe relevant constituents in the composition is preferably 80% or more,particularly preferably 90% or more and very particularly preferably 95%or more, and

[0082] consist virtually completely of means that the concentration ofthe relevant constituents in the composition is preferably 98% or more,particularly preferably 99% or more and very particularly preferably100.0%.

[0083] This applies both to the media as compositions with theirconstituents, which may be components and compounds, and to thecomponents with their constituents, those of the compounds.

[0084] The liquid-crystal media preferably comprise one or morecompounds selected from the group consisting of the compounds of theformulae I-1, I-2 and I-4, particularly preferably of the formulae I-2and/or I-4.

[0085] Component B preferably consists predominantly, particularlypreferably consists essentially completely and very particularlypreferably consists virtually completely, of one or more compoundsselected from the group consisting of the compounds of the formulae IIand III.

[0086] The compounds of the formula II are preferably selected from thegroup consisting of the compounds of the formulae II-1 to II-3

[0087] in which

[0088] R²¹ and R²² are as defined above under the formula I, and

[0089] R²¹ is preferably n-alkyl having from 1 to 7 atoms, n-alkoxyhaving from 1 to 7 carbon atoms or alkenyloxy having from 2 to 7 carbonatoms, and

[0090] R²² is preferably n-alkoxy having from 1 to 7 carbon atoms oralkenyloxy having from 2 to 7 carbon atoms, and in the formulae I2 andI3 is alternatively n-alkyl having from 1 to 7 carbon atoms,

[0091]  in which

[0092]  preferably

[0093] n is 0 or1.

[0094] The compounds of the formula III are preferably selected from thegroup consisting of the compounds of the formulae III-1 and III-2:

[0095] in which

[0096] R³¹ and R³² are as defined above under the formula III and arepreferably n-alkyl.

[0097] The liquid-crystal media particularly preferably comprise one ormore compounds selected from the group consisting of the compounds ofthe formulae II-1a to II-1f:

[0098] in which R²¹ and R²² are as defined above in the case of theformula II and are preferably as defined above in the case of theformula II-1.

[0099] The liquid-crystal media particularly preferably comprise one ormore compounds selected from the group consisting of the compounds ofthe formulae II-2a to II-2c:

[0100] in which R²¹ and R²² are as defined above in the case of theformula II and are preferably as defined above in the case of theformula II-2.

[0101] The liquid-crystal media particularly preferably comprise one ormore compounds of the formula II-3a

[0102] in which R²¹ and R²² are as defined above in the case of theformula II and are preferably as defined above in the case of theformula II-3.

[0103] Component C preferably consists predominantly, particularlypreferably consists essentially completely and very particularlypreferably consists virtually completely, of one or more compounds ofthe formula IV. These compounds of the formula IV are preferablyselected from the group consisting of the compounds of the formulae IV-1to IV-3:

[0104] in which R⁴¹, R⁴², Z⁴¹, Z⁴²,

[0105] are each as correspondingly defined above in the case of theformula IV.

[0106] The liquid-crystal medium especially preferably comprises one ormore compounds selected from the group consisting of the compounds ofthe formulae IV-1a to IV-1d, IV-1e, IV-2a to IV-2e and IV-3a to IV-3c:

[0107] in which n and m are each, independently of one another, from 1to 5, and o and p are each, independently thereof and from one another,from 0 to 3,

[0108] in which R⁴¹ and R⁴² are each as defined above under the formulaIV1, and the phenyl rings may optionally be fluorinated, but not in sucha way that the compounds are identical with those of the formula II andits sub-formulae. R⁴¹ is preferably n-alkyl having from 1 to 5 carbonatoms, particularly preferably having from 1 to 3 carbon atoms, and R⁴²is preferably n-alkyl or n-alkoxy having from 1 to 5 carbon atoms oralkenyl having from 2 to 5 carbon atoms. Of these, particular preferenceis given to the compounds of the formulae IV1a to IV1 d.

[0109] Component D preferably consists predominantly, particularlypreferably consists essentially completely and very particularlypreferably consists virtually completely, of one or more compounds ofthe formula IV. These compounds of the formula IV are preferablyselected from the group consisting of the compounds of the formulae V-1to V-4:

[0110] in which R⁵, Z⁵², Z⁵³ and

[0111] are as defined above for the formula V, but preferably

[0112] R⁵ is alkyl having 1-7 carbon atoms or alkenyl having 2-7 carbonatoms, preferably vinyl or 1E-alkenyl,

[0113]  one of

[0114] Z⁵² and Z⁵³ is a single bond and the other is —CH₂CH₂—, —COO— ora single bond and

[0115] In a preferred embodiment, the medium comprises one or morecompounds of the formula VI, preferably selected from the groupconsisting of the compounds of the formulae VI-1 to VI-4:

[0116] in which R⁶¹ and R⁶² are as defined above in the case of theformula VI.

[0117] In a preferred embodiment, the medium comprises one or morecompounds of the formula VII, preferably from the group consisting ofthe formula VII-1

[0118] in which

[0119] R⁷¹ and R⁷² are as defined above in the case of the formula VII.

[0120] In a preferred embodiment, the liquid-crystal media according tothe invention comprise in total, based on the mixture as a whole,

[0121] from 5% to 85%, preferably from 10% to 55% and particularlypreferably from 15% to 40%, of component A, preferably of compounds ofthe formula I,

[0122] from 5% to 85%, preferably from 10% to 85%, particularlypreferably from 20% to 80% and very particularly preferably from 40% to75%, of component B, preferably of compounds of the formulae II and III,where the ratio of the concentrations of compounds II and III ispreferably greater than or equal to 2:1, particular preferably greaterthan or equal to 3:1 and very particularly preferably greater than orequal to 4:1,

[0123] from 0% to 50%, preferably from 0% to 40%, particularlypreferably from 0% to 30% and very particularly preferably from 5% to25%, of component C, preferably of compounds of the formula IV, and

[0124] from 0% to 40%, preferably from 0% to 30%, particularlypreferably from 0% to 20%, and very particularly preferably from 1% to15%, of component D, preferably of compounds of the formula IV.

[0125] Here, as throughout the present application, the term compounds,also written as compound(s), means both one and a plurality ofcompounds, unless explicitly stated otherwise.

[0126] The individual compounds are employed here in concentrations ofin each case from 1% to 30%, preferably from 2% to 30% and particularlypreferably from 4% to 16%. An exception is formed here by compoundshaving three phenyl rings and compounds having four six-membered rings.These compounds are employed in concentrations of in each case from 0.5%to 15%, preferably from 1% to 10% and particularly preferably from 1% to8% per individual compound. In the case of compounds of the formula I inwhich n=0, the preferred limits to the concentrations for the proportionof the individual compounds in the medium are from 1% to 20%, preferablyfrom 2% to 15% and particularly preferably from 5% to 8%. In the case ofthe compounds of the formula I in which n=1, the preferred limits to theconcentrations for the proportion of the individual compounds in themedium are from 1% to 30%, preferably from 2% to 20% and particularlypreferably from 8% to 12%.

[0127] In a preferred embodiment, the liquid-crystal media particularlypreferably comprise in total

[0128] from 10% to 40% of compounds of the formula I,

[0129] from 50% to 90% of compounds of the formulae II and III,

[0130] from 0% to 40% of compounds of the formula IV, and

[0131] from 0% to 20% of compounds of the formula V.

[0132] In this embodiment, the liquid-crystal media very particularlypreferably comprise in total

[0133] from 15% to 35% of compounds of the formula I,

[0134] from 60% to 80% of compounds of the formulae II and III,

[0135] from 0% to 20% of compounds of the formula IV and

[0136] from 0% to 5% of compounds of the formula V.

[0137] In a particularly preferred embodiment, which may be identicaland preferably is identical with the preferred embodiments describedabove for the preferred concentration ranges, the liquid-crystal mediacomprise:

[0138] one or more compounds of the formula I, preferably selected fromthe group consisting of the compounds of the formulae I-1b and I-7a,preferably in which R¹¹ is n-alkyl and R¹² is alkoxy, and

[0139] one or more compounds of the formula II-1, preferably

[0140] one or more compounds of the formula II-1a, and/or, preferablyand,

[0141] one or more compounds of the formula II-1c, and/or, preferablyand,

[0142] one or more compounds of the formula III-1, and/or, preferablyand,

[0143] one or more compounds selected from the group consisting of thecompounds of the formulae IV-1 to IV-4, preferably

[0144] one or more compounds of the formula IV-1 selected from the groupconsisting of the compounds of the formulae IV-1a to IV-1d, veryparticularly preferably selected from the group consisting of theformulae IV-1c and IV-1d and in particular of the formula IV-1c, and/or,preferably and,

[0145] one or more compounds of the formula IV-2c and/or IV-2e, and/or,preferably and,

[0146] one or more compounds of the formula IV-3c and/or IV-3d, and/or,preferably and,

[0147] one or more compounds of the formula IV-4, and/or

[0148] one or more compounds selected from the group consisting of thecompounds of the formulae V to VII.

[0149] Particular preference is given here to liquid-crystal media whichcomprise

[0150] one or more compounds of the formula I, preferably selected fromthe group consisting of the compounds of the formulae I-1b and I-7a,preferably in which R¹¹ is n-alkyl and R¹² is alkoxy, and in particularin each case in concentrations of from 6% to 20% per compound, and/or

[0151] one or more compounds of the formula II-1a, in particular in eachcase in concentrations of from 4% to 18% per compound, and/or

[0152] one or more compounds of the formula II-1c, in particular in eachcase in concentrations of from 3% to 15% per compound, preferably ineach case one or more compounds in which R²¹ is alkyl having from 1 to 3carbon atoms and R²² is alkoxy having from 1 to 3 carbon atoms, and inwhich R²¹ is alkyl having from 1 to 3 carbon atoms and R²² is alkylhaving from 1 to 3 carbon atoms, and/or

[0153] one or more compounds of the formula IV-1, preferably of theformulae IV-1b and/or IV-1c.

[0154] These media may, if desired, comprise one or more compoundsselected from the group consisting of the compounds of the formulae V-1to V-4.

[0155] The liquid-crystal media according to the invention preferablyhave nematic phases of in each case from −20° C. to 70° C., particularlypreferably from −30° C. to 80° C. and very particularly preferably from−40° C. to 90° C. and most preferably from −40° C. to 105° C.

[0156] The term “have a nematic phase” here means firstly that nosmectic phase and no crystallisation are observed at low temperatures atthe corresponding temperature and secondly also that no clearing occurson heating from the nematic phase. The investigation at low temperaturesis carried out in a flow viscometer at the corresponding temperature andchecked by storage for at least 100 hours in test cells having a layerthickness corresponding to the electro-optical application. At hightemperatures, the clearing point is measured in capillaries byconventional methods.

[0157] Furthermore, the liquid-crystal media according to the inventionare characterised by relatively low optical anisotropy values. Thebirefringence values are preferably in the range from 0.060 to 0.150,particularly preferably in the range from 0.070 to 0.120 and veryparticularly preferably in the range from 0.070 to 0.110.

[0158] In addition, the liquid-crystal media according to the inventionhave relatively low values for the threshold voltage (V₀) of less thanor equal to 2.2 V, preferably less than or equal to 2.0 V, particularlypreferably less than or equal to 1.9 V and very particularly preferablyless than or equal to 1.85 V. In a particularly preferred embodiment,the liquid-crystal media according to the invention have values for thethreshold voltage which are less than or equal to 1.5 V.

[0159] These preferred values for the individual physical properties arealso observed in each case in combination with one another.

[0160] Independently of the above-mentioned dimensioning limits for thecompounds of the formulae I, II and III, compounds of the formulae I andII are employed in the liquid-crystal media in accordance with thepresent invention in a concentration of up to about 25% per individualsubstance, and compounds of the formula III are employed in aconcentration of up to about 20%, preferably up to 16%, per individualsubstance. Compounds of the formula I-1 are preferably employed inconcentrations of up to about 20%, preferably up to 15%, per individualsubstance.

[0161] In the present application, “≦” means less than or equal to,preferably less than, and “≧” means greater than or equal to, preferablygreater than.

[0162] In the present application,

[0163] denote trans-1,4-cyclohexylen.

[0164] In the present application, the term dielectrically positivecompounds means compounds having a Δε of >1.5, dielectrically neutralcompounds means those in which −1.5≦Δε≦1.5, and dielectrically negativecompounds means those having a Δε<−1.5. The dielectric anisotropy of thecompounds is determined here by dissolving 10% of the compounds in aliquid-crystalline host and determining the capacitance of this mixtureat 1 kHz in at least one test cell having a thickness of 20 μm with ahomeotropic surface alignment and in at least one test cell having athickness of 20 μm with a homogeneous surface alignment. The measurementvoltage is typically from 0.5 V to 1.0 V, but is always less than thecapacitive threshold of the respective liquid-crystal mixture.

[0165] The host mixture used for dielectrically positive anddielectrically neutral compounds is ZLI-4792 and the host mixture usedfor dielectrically negative compounds is ZLI-2857, both from Merck KGaA,Germany. The change in the dielectric constants of the host mixtureafter addition of the compound to be investigated and extrapolation to100% of the compound employed gives the values for the respectivecompounds to be investigated.

[0166] The term threshold voltage usually relates to the opticalthreshold for 10% relative contrast (V₁₀), unless explicitly statedotherwise.

[0167] In relation to the liquid-crystal mixtures of negative dielectricanisotropy, however, the term threshold voltage in the presentapplication is used for the capacitive threshold voltage (V₀), alsoknown as the Freedericksz threshold, unless explicitly stated otherwise.

[0168] All concentrations in this application, unless explicitly statedotherwise, are given in percent by weight and relate to thecorresponding mixture or mixture component. All physical properties areand have been determined in accordance with “Merck Liquid Crystals,Physical Properties of Liquid Crystals”, status November 1997, MerckKGaA, Germany, and apply to a temperature of 20° C., unless explicitlystated otherwise. Δn is determined at 589 nm and Δε at 1 kHz.

[0169] In the case of the liquid-crystal media of negative dielectricanisotropy, the threshold voltage was determined as the capacitivethreshold V₀ (also known as the Freedericksz threshold) in test cellsproduced at Merck KgaA, Germany, with a liquid-crystal alignedhomeotropically by means of lecithin.

[0170] The liquid-crystal media according to the invention may, ifnecessary, also comprise further additives and chiral dopants in theconventional amounts. The amount of these additives employed is in totalfrom 0% to 10%, based on the amount of the mixture as a whole,preferably from 0.1% to 6%. The concentrations of the individualcompounds employed are preferably from 0.1 to 3%. The concentration ofthese and similar additives is not taken into account when indicatingthe concentrations and the concentration ranges of the liquid-crystalcompounds in the liquid-crystal media.

[0171] The compositions consist of a plurality of compounds, preferablyfrom 3 to 30, particularly preferably from 6 to 20 and very particularlypreferably from 10 to 16 compounds, which are mixed in a conventionalmanner. In general, the desired amount of the components used in smalleramount is dissolved in the components making up the principalconstituent, advantageously at elevated temperature. If the selectedtemperature is above the clearing point of the principal constituent,the completion of the dissolution process is particularly easy toobserve. However, it is also possible to prepare the liquid-crystalmixtures in other conventional ways, for example using premixes or froma so-called “multibottle system”.

[0172] By means of suitable additives, the liquid-crystal phasesaccording to the invention can be modified in such a way that they canbe employed in any type of ECB, VAN, IPS, GH or ASM-PA LCD display thathas been disclosed hitherto.

[0173] The entire disclosure[s] of all applications, patents andpublications, cited above or below, and of corresponding Germanapplication No.10063943.7, filed Dec. 20, 2000, is hereby incorporatedby reference.

EXAMPLES

[0174] The examples below serve to illustrate the invention withoutrepresenting a limitation. In the examples, the melting point T (C, N),the transition from the smectic (S) phase to the nematic (N) phase T(S,N) and the clearing point T (N, I) of a liquid-crystal substance areindicated in degrees Celsius.

[0175] Unless explicitly stated otherwise, the percentages above andbelow are percent by weight, and the physical properties are the valuesat 20° C., unless explicitly stated otherwise.

[0176] All the indicated values for temperatures in this application are°C. and all temperature differences are correspondingly differentialdegrees, unless explicitly stated otherwise.

[0177] In the present application and in the examples below, thestructures of the liquid-crystal compounds are indicated by means ofacronyms, the transformation into chemical formulae taking place inaccordance with Tables A and B below. All radicals C_(n)H_(2n+1) andC_(m)H_(2m−1) are straight-chain alkyl radicals having n and m carbonatoms respectively. The coding in Table B is self-evident. In Table A,only the acronym for the parent structure is indicated. In individualcases, the acronym for the parent structure is followed, separated by ahyphen, by a code for the substituents R¹, R², L¹ and L²: Code for R¹,R², L¹, L², L³ R¹ R² L¹ L² L³ nm C_(n)H_(2n+1) C_(m)H_(2m+1) H H H nOmC_(n)H_(2n+1) OC_(m)H_(2m+1) H H H nO.m OC_(n)H_(2n+1) C_(m)H_(2m+1) H HH nmFF C_(n)H_(2n+1) C_(m)H_(2m+1) H F F nmOFF C_(n)H_(2n+1)OC_(m)H_(2m+1) H F F n C_(n)H_(2n+1) CN H H H nN.F C_(n)H_(2n+1) CN F HH nN.F.F C_(n)H_(2n+1) CN F F H nF C_(n)H_(2n+1) F H H H nF.FC_(n)H_(2n+1) F F H H nF.F.F C_(n)H_(2n+1) F F F H nOF OC_(n)H_(2n+1) FH H H nCl C_(n)H_(2n+1) Cl H H H nCl.F C_(n)H_(2n+1) Cl F H H nCl.F.FC_(n)H_(2n+1) Cl F F H nCF₃ C_(n)H_(2n+1) CF₃ H H H nCF₃.F C_(n)H_(2n+1)CF₃ F H H nCF₃.F.F C_(n)H_(2n+1) CF₃ F F H nOCF₃ C_(n)H_(2n+1) OCF₃ H HH nOCF₃.F C_(n)H_(2n+1) OCF₃ F H H nOCF₃.F.F C_(n)H_(2n+1) OCF₃ F F HnOCF₂ C_(n)H_(2n+1) OCHF₂ H H H nOCF₂.F C_(n)H_(2n+1) OCHF₂ F H HnOCF₂.F.F C_(n)H_(2n+1) OCHF₂ F F H nS C_(n)H_(2n+1) NCS H H H nS.FC_(n)H_(2n+1) NCS F H H nS.F.F C_(n)H_(2n+1) NCS F F H rVsNC_(r)H_(2r+1)—CH═CH—C_(s)H_(2s)— CN H H H rEsNC_(r)H_(2r+1)—O—C_(s)H_(2s)— CN H H H

[0178] TABLE A

PCH EPCH

BCH CCP

CECP ECCP

BECH EBCH

PTP CPTP

CEPTP

CCH PDX

PYP PYRP

D ME

HP CP

EHP

ET

[0179] TABLE B

CCZU-n-X CDU-n-X (X = F, Cl or OCF₃) (X = F, Cl or OCF₃)

K3-n M3-n

G3-n T3-n

Inm

BCH-n.FX CGU-n-X (X = F, Cl or OCF₃) (X = F, Cl or OCF₃)

C-nm

CB15 C15

CCN-nm NCB-nm

CCEPC-nm

CCPC-nm

CH-nm

HD-nm

HH-nm

OS-nm

CHE

BCH-nmF

CBC-nm(F)

ECBC-nm

ECCH-nm CCH-n1Em

T-nFx B-nO.FX (X = F, Cl or OCF₃) (X = F, Cl or OCF₃)

PGIGI-n-X GGP-n-X (X = F, Cl or OCF₃) (X = F, Cl or OCF₃)

CVCC-n-m

CVCP-n-m

CVCVC-n-m

CP-V-N

CCG-V-F

CCP-V-n

CCP-Vn-m

CPP-V-m

CPP-nV-m

CPP-Vn-m

CC-n-V

CC-n-Vm

CC-n-mV

CC-V-V

CC-V-Vn

CC-nV-Vm

CC-V-nV

CC-Vn-mV

CC-nV-Vm

PCH-n(O)mFF

CCP-n(O)mFF

CCY-nO-Om

CCY-VO-(O)m

CCY-VnO-(O)m

CPY-n-(O)m

CPY-nO-(O)m

CPY-V-(O)m

CPY-VO-(O)m

CPY-Vn-(O)m

CPY-VnO-(O)m

CLY-n-(O)m

CLY-nO-(O)m

CFY-n-(O)m

CFY-nO-(O)m

YY-n-(O)m

YY-nO-Om

CQY-n-(O)m

CCQY-n-(O)m

CPQIY-n-(O)m

CQPY-n-(O)m

PQPY-n-(O)m

[0180] The following examples are intended to illustrate the inventionwithout representing a limitation. Above and below, percentages arepercent by weight. All temperatures are indicated in degrees Celsius. Δndenotes optical anisotropy (589 nm, 20° C.), Δε denotes the dielectricanisotropy (1 kHz, 20° C.), H.R. denotes the voltage holding ratio (at100° C., after 5 minutes in the oven, 1 V), and V₀, the thresholdvoltage, was determined at 20° C.

Example 1

[0181] Compound/ Concentration/ abbreviation % by weight Physicalproperties CPQIY-3-O2 10.0 T (N, I) = 105.5° C. CPQIY-3-O4 10.0 n_(e)(20° C., 589 nm) = 1.5822 CPQIY-5-O4 10.0 Δn (20° C., 589 nm) = 0.1001PCH-304FF 9.0 ε_(⊥) (20° C., 1 kHz) = 8.3 PCH-504FF 9.0 Δε (20° C., 1kHz) = −4.6 CCP-202FF 4.0 γ₁ (20° C.) = 271 mPa · s CCP-302FF 6.0t_(store) (−40° C.) > 1000 h CCP-502FF 6.0 VHR (5 min, 100° C.) = 89%CCP-21FF 7.0 V₀ (20° C.) = 2.25 V CCP-31FF 10.0 CCP-V-1 9.0 CC-3-V1 10.0Σ 100.0

[0182] The liquid-crystal medium is introduced into a VA display withTFT addressing. This display is distinguished, in particular, by thefact that it can be employed in a very large temperature range, asrequired for so-called broad range applications, for example in mobiletelephones and in navigation systems.

Example 2

[0183] Compound/ Concentration/ abbreviation % by weight Physicalproperties CPQIY-3-O2 10.0 T (N, I) = 71.5° C. CPQIY-3-O4 6.0 n_(e) (20°C., 589 nm) = 1.5773 CPQIY-5-O4 8.0 Δn (20° C., 589 nm) = 0.0947 D-302FF20.0 ε_(⊥) (20° C., 1 kHz) = 11.7 D-502FF 20.0 Δε (20° C., 1 kHz) = −7.5PCH-502FF 14.0 γ₁ (20° C.) = 268 mPa · s PCH-504FF 11.0 t_(store) (−20°C.) > 1000 h CCP-302FF 5.0 t_(store) (−40° C.) ≧ 500 h CCP-502FF 6.0 V₀(20° C.) = 1.45 V Σ 100.0

[0184] As in Example 1, the liquid-crystal medium is introduced into adisplay having TFT addressing, but here into an IPS display. Thisdisplay is distinguished, in particular, by a very low addressingvoltage.

Example 3

[0185] Compound/ Concentration/ abbreviation % by weight Physicalproperties CPQIY-3-O4 8.0 T (N, I) = 71.0° C. CPQIY-5-O4 8.0 n_(e) (20°C., 589 nm) = 1.5788 CCQY-5-O2 5.3 Δn (20° C., 589 nm) = 0.1007PCH-304FF 19.0 ε_(⊥) (20° C., 1 kHz) = 8.5 PCH-502FF 9.0 Δε (20° C., 1kHz) = −4.4 PCH-504FF 14.0 γ₁ (20° C.) = 219 mPa · s CCP-302FF 13.7 k₁(20° C.) = 11.8 pN BCH-32 8.0 k₁ /k₃(20° C.) = 1.24 CC-5-V 3.0 t_(store)(−30° C.) > 1000 h CC-3-V1 8.0 t_(store) (−40° C.) > 1000 h PGIGI-3-F4.0 V₀ (20° C.) = 1.92 V Σ 100.0

[0186] As in Example 1, the liquid-crystal-medium is introduced into aVA display with TFT addressing.

Example 4

[0187] Compound/ Concentration/ abbreviation % by weight Physicalproperties CCQY-5-O2 7.0 T (N, I) = 99.0° C. PCH-304FF 12.0 n_(e) (20°C., 589 nm) = 1.5825 PCH-502FF 9.0 Δn (20° C., 589 nm) = 0.1003PCH-504FF 13.0 ε_(⊥) (20° C., 1 kHz) = 8.1 CCP-302FF 11.0 Δε (20° C., 1kHz) = −4.4 CCP-502FF 9.0 γ₁ (20° C.) = 266 mPa · s CCP-21FF 7.0 k₁ (20°C.) = 16.7 pN CCP-31FF 11.0 k₁ /k₃(20° C.) = 1.13 BCH-32 8.0 t_(store)(−30° C.) > 1000 h CCP-V-1 10.0 t_(store) (−40° C.) ≧ 300 h CC-3-V1 3.0V₀ (20° C.) = 2.21 V Σ 100.0

[0188] As in Example 1, the liquid-crystal medium is introduced into aVA display with TFT addressing. This display is distinguished, inparticular, by the fact that it can be employed in a very largetemperature range, as required for so-called broad range applications,for example in mobile telephones and in navigation systems.

Example 5

[0189] Compound/ Concentration/ abbreviation % by weight Physicalproperties CPQIY-3-O4 10.0 T (N, I) = 70.5° C. CPQIY-5-O4 10.0 n_(e)(20° C., 589 nm) = 1.5785 PCH-304FF 17.0 Δn (20° C., 589 nm) = 0.0993PCH-502FF 9.0 ε_(⊥) (20° C., 1 kHz) = 8.1 PCH-504FF 14.0 Δε (20° C., 1kHz) = −4.2 CPY-2-O2 7.0 γ₁ (20° C.) = 187 mPa · s CPY-3-O2 7.0 k₁ (20°C.) = 11.5 pN CCP-V-1 12.0 k₁ /k₃(20° C.) = 1.24 CCH-35 5.0 t_(store)(−30° C.) > 1000 h CC-3-V1 9.0 t_(store) (−40° C.) ≧ 300 h Σ 100.0 V₀(20° C.) = 1.95 V

[0190] As in Example 1, the liquid-crystal medium is introduced into aVA display with TFT addressing.

Example 6

[0191] Compound/ Concentration/ abbreviation % by weight Physicalproperties PQPY-5-O4 14.0 T (N, I) = 71.0° C. PCH-304FF 16.0 n_(e) (20°C., 589 nm) = 1.5812 PCH-502FF 12.0 Δn (20° C., 589 nm) = 0.1023PCH-504FF 3.0 ε_(⊥) (20° C., 1 kHz) = 6.9 CPY-2-O2 7.0 Δε (20° C., 1kHz) = −3.3 CPY-3-O2 7.0 γ₁ (20° C.) = 108 mPa · s CCP-V-1 4.0 t_(store)(−30° C.) > 1000 h BCH-32 7.0 t_(store) (−40° C.) > 1000 h CCH-35 5.0 V₀(20° C.) = 2.10 V CC-3-V 4.0 CC-5-V 11.0 CC-3-V1 10.0 Σ 100.0

[0192] As in Example 1, the liquid-crystal medium is introduced into aVA display with TFT addressing. This display exhibits, in particular,very short response times.

Example 7

[0193] Compound/ Concentration/ abbreviation % by weight Physicalproperties PQPY-5-1 10.0 T (N, I) = 72.0° C. PCH-304FF 18.0 n_(e) (20°C., 589 nm) = 1.5890 PCH-502FF 12.0 Δn (20° C., 589 nm) = 0.1054PCH-504FF 4.0 ε_(⊥) (20° C., 1 kHz) = 6.9 CCP-31FF 6.0 Δε (20° C., 1kHz) = −3.3 CPY-2-O2 4.0 γ₁ (20° C.) = 112 mPa · s CPY-V-O2 10.0t_(store) (−30° C.) > 1000 h CCP-V-1 7.0 t_(store) (−40° C.) > 1000 hCCP-V2-1 3.0 V₀ (20° C.) = 2.14 V BCH-32 6.0 CC-3-V 9.0 CC-3-2V 6.0CC-3-V1 5.0 Σ 100.0

[0194] As in Example 1, the liquid-crystal medium is introduced into aVA display with TFT addressing. This display exhibits, in particular,very short response times.

Example 8

[0195] Compound/ Concentration/ abbreviation % by weight Physicalproperties PQPY-5-O2 20.0 T (N, I) = 86.5° C. PCH-304FF 14.0 n_(e) (20°C., 589 nm) = 1.5930 PCH-502FF 10.0 Δn (20° C., 589 nm) = 0.1109PCH-504FF 13.0 ε_(⊥) (20° C., 1 kHz) = 9.0 CCP-302FF 9.0 Δε (20° C., 1kHz) = −5.1 CCP-502FF 8.0 γ₁ (20° C.) = 239 mPa · s CCP-21FF 3.0t_(store) (−20° C.) > 1000 h CCP-31FF 6.0 t_(store) (−30° C.) ≧ 900 hBCH-32 6.0 t_(store) (−40° C.) ≧ 600 h CCP-V-1 7.0 V₀ (20° C.) = 1.90 VCC-3-V1 5.0 Σ 100.0

[0196] As in Example 1, the liquid-crystal medium is introduced into aVA display with TFT addressing. This display is distinguished, inparticular, by the fact that it can be employed in a large temperaturerange and a low addressing voltage is required.

Example 9

[0197] Compound/ Concentration/ abbreviation % by weight Physicalproperties CQPY-5-O2 11.0 T (N, I) = 86.5° C. PCH-304FF 13.0 n_(e) (20°C., 589 nm) = 1.5971 PCH-502FF 12.0 Δn (20° C., 589 nm) = 0.1080PCH-504FF 16.0 ε_(⊥) (20° C., 1 kHz) = 9.0 CCP-302FF 12.0 Δε (20° C., 1kHz) = −5.2 CCP-502FF 13.0 γ₁ (20° C.) = 262 mPa · s CCP-21FF 8.0t_(store) (−20° C.) > 1000 h BCH-32 8.0 t_(store) (−30° C.) ≧ 800 hCCP-V-1 4.0 t_(store) (−40° C.) ≧ 500 h PGIGI-3-F 3.0 V₀ (20° C.) = 1.90V Σ 100.0

[0198] As in Example 1, the liquid-crystal medium is introduced into aVA display with TFT addressing. This display is distinguished, inparticular, by the fact that it can be employed in a large temperaturerange.

Example 10

[0199] Compound/ Concentration/ abbreviation % by weight Physicalproperties CQY-5-O2 12.0 T (N, I) = 70° C. PCH-304FF 18.0 n_(e) (20° C.,589 nm) = 1.5850 PCH-502FF 9.0 Δn (20° C., 589 nm) = 0.1011 CPY-2-O313.0 ε_(⊥) (20° C., 1 kHz) = 6.9 CPY-3-O3 13.0 Δε (20° C., 1 kHz) = −3.3BCH-32 6.0 γ₁ (20° C.) = 115 mPa · s CCP-V-1 2.0 t_(store) (−40° C.) >1000 h CC-5-V 18.0 V₀ (20° C.) = 2.10 V CC-3-V1 9.0 Σ 100.0

[0200] As in Example 1, the liquid-crystal medium is introduced into aVA display with TFT addressing. This display is distinguished, inparticular, by very short response times.

Example 11

[0201] Compound/ Concentration/ abbreviation % by weight Physicalproperties CQY-5-O2 13.0 T(N,I) = 71.0 ° C. PCH-304FF 10.0 Δn (20° C.,589 nm) = 0.0792 PCH-502FF 13.0 ε_(⊥) (20° C., 1 kHz) = 8.0 PCH-504FF14.0 Δε (20° C., 1 kHz) = −4.2 CCP-302FF 11.0 γ₁ (20° C.) = 140 mPa·sCCP-502FF 14.0 V₀ (20° C.) = 2.0 V CCH-35 8.0 CC-3-V1 9.0 CC-5-V 5.0CCP-V1 3.0 Σ 100.0

[0202] As in Example 1, the liquid-crystal medium is introduced into aVA display with TFT addressing. This display is distinguished, inparticular, by very short response times.

[0203] The liquid-crystal mixtures of Examples 1 and 3 to 11 can also beused with good results in IPS displays.

1. A nematic liquid-crystal medium, which comprises a) a dielectricallynegative, liquid-crystalline component A which comprises one or moredielectrically negative compounds of the formula I

 in which

 and are, independently of one another,

R¹¹ is alkyl having from 1 to 7 carbon atoms, alkoxy having from 1 to 7carbon atoms or alkenyloxy having from 2 to 7 carbon atoms, R¹² is alkylor alkoxy having from 1 to 7 carbon atoms or alkenyl, alkenyloxy oralkoxyalkyl having from 2 to 7 carbon atoms, one of Z¹¹ and Z¹² is OCF₂or CF₂O, and the other is a single bond, and n is 0 or 1, and b) adielectrically negative, liquid-crystalline component, B and c) adielectrically neutral, liquid-crystalline component C, and d) adielectrically positive, liquid-crystalline component D.
 2. Aliquid-crystal medium of claim 1, wherein component B comprises one ormore compounds selected from the group consisting of the compounds ofthe formulae II and III

in which R²¹ is alkyl or alkoxy having from 1 to 7 carbon atoms oralkoxyalkyl, alkenyl or alkenyloxy having from 2 to 7 carbon atoms, R²²is alkyl or alkoxy having from 1 to 7 carbon atoms or alkoxyalkyl,alkenyl or alkenyloxy having from 2 to 7 carbon atoms, Z²¹ and Z²² areeach, independently of one another, —CH₂—CH₂—, —CH═CH—, —C≡C—, —COO— ora single bond,

 and

 are each, independently of one another,

L²¹ and L²² are both C—F or one of the two is N and the other is C—F, mis 0 or 1, Z³ is —CH₂—CH₂—, —CH═CH—, —C≡C—, —COO— or a single bond, R³¹and R³² are each, independently of one another, alkyl or alkoxy havingfrom 1 to 7 carbon atoms or alkoxy-alkyl, alkenyl or alkenyloxy havingfrom 2 to 7 carbon atoms, and I is 1 or
 2. 3. A liquid-crystal medium ofclaim 2, which comprises one or more compounds of the formula II.
 4. Aliquid-crystal medium of claim 2 which comprises one or more compoundsof the formula III.
 5. A liquid-crystal medium of claim 1 whichcomprises a component C.
 6. A liquid-crystal medium of claim 1, whichcomprises a component D.
 7. An electro-optical display comprising aliquid-crystal medium according of claim
 1. 8. A display according toclaim 7, which is an active matrix display.
 9. A display according toclaim 7 which is an ECB or IPS display.
 10. The liquid-crystal medium ofclaim 1, wherein R¹¹ is alkyl, alkoxy, or alkenyloxy of Z to 4 carbonatoms and one of Z¹¹ or Z¹² is OCF₂.
 11. The liquid-crystal medium ofclaim 5, wherein component C comprises at least one compound of theformula IV.

in which R⁴¹ and R⁴² are each, independently of one another, as definedabove for R²¹ in the case of the formula II, Z⁴¹, Z⁴² and Z⁴³ are each,independently of one another, —CH₂CH₂—, —CH═CH—, —COO— or a single bond,

 are each, independently of one another,

 o and p, independently of one another, are 0 or 1,
 12. Theliquid-crystal medium of claim 6, wherein component D comprises at leastone compound of the formula V.

are each, independently of one another,

and very particularly preferably at least two of these rings

where two adjacent rings are very particularly preferably linkeddirectly to one another, preferably

and optionally d) one or more dielectric positive compound(s) of theformula V

R⁵ is alkyl or alkoxy having from 1 to 7 carbon atoms, or alkoxyalkyl,alkenyl or alkenyloxy having from 2 to 7 carbon atoms, Z⁵¹, Z⁵² and Z⁵³are each, independently of one another, —CH₂—CH₂—, —CH═CH—, —C≡C—, —COO—or a single bond,

 are each, independently of one another,

X⁵ is F, OCF₂H or OCF₃, and Y⁵ is H or F, preferably F in the case whereX=F or OCF₂H, and q and r are each, independently of one another, 0or
 1. In a further preferred embodiment, the medium comprises one ormore dielectrically negative compounds of the formula VI.
 13. Theliquid-crystal medium of claim 1, which comprises 5% to 85% by weight ofcomponent A, 5% to 85% by weight of component B, 0 to 50% by weight ofcomponent C and 0 to 40% by weight of component D.
 14. A. displayaccording to claim 8, which further comprises a this film transistor orvaristor.
 15. A display according to claim 7, which further comprises athree-pole switching element.